Electrohydrodynamic spraying

ABSTRACT

A small area electrostatic aerosol collector combines electrostatic collection of aerosol particles and electrohydrodynamic spraying of fluid so that a sample collected electrostatically can have fluid applied thereto. The fluid may assist with disaggregation and/or desalinization of biological material collected onto a sample substrate. A controller associated with the collector may control an electrostatic charge device and a spraying device such that the charge device and spraying device may operate in alternating fashion, or the charge device and spraying device may operate simultaneously. Further, mechanical systems are provided, for the disaggregation of particulate clusters collected onto a sample substrate.

TECHNICAL FIELD

The present invention relates to collectors for the separation andcollection of particulates from a fluid stream, and more particularly,to systems and methods that: combine electrostatic particle collectionand electrohydrodynamic fluid spraying, provide electrohydrodynamicspraying inside a nozzle, provide for the application ofelectrohydrodynamic spraying to the disaggregation and desalination ofcollected samples, or combinations thereof.

BACKGROUND ART

The monitoring of airborne bioaerosols has received an increasing amountof attention in recent years because of the potential impact ofparticulates on radiative and climatic processes, on human health andbecause of the role particles play in atmospheric transport anddeposition of pollutants. For example, it may be desirable to analyzethe air in a predetermined location for particulates that fall within arange of sizes that can be inhaled, such as naturally occurring orartificially produced airborne pathogens, allergens, bacteria, viruses,fungi and biological or chemical agents that are found in or areotherwise introduced into the location.

As another example, it may be desirable to detect the presence ofparticular airborne particulates in semiconductor clean rooms,pharmaceutical production facilities and biotechnology laboratories toverify that there has been no contamination produced in suchenvironments that would create undesirable environmental exposures oradversely affect manufacturing, testing or experimental processes.Similarly, the ability to detect the presence of particular airborneparticulates in hospitals, nursing homes, rehabilitation centers andother care facilities may be beneficial to assist in preventing thespread of disease, infection or harmful bacteria.

The monitoring of atmospheric particulate matter further findsapplication for assessments of human health risk, environmentalcontamination and for compliance with National Air Quality Standards(NAAQS), e.g., to monitor the air in public and commercial building airpurification and distribution systems; work sites such as mines, sewagefacilities, agricultural and manufacturing facilities; outside areassuch as street corners, flues and smokestacks; and other locations whereit is desirable to monitor environmental hygiene, such as residencesexposed to microorganisms, plants or animals.

DISCLOSURE OF INVENTION

According to various aspects of the present invention, a small areaelectrostatic aerosol collector comprises a collector housing, anaerosol entry port that provides an inlet for air to flow from outsideof the collector housing to the inside of the housing, and a samplesubstrate receiving area within the collector housing for receiving asample substrate upon which particulates are collected. Moreover, apassageway is provided between the aerosol entry port and the samplesubstrate receiving area.

Still further, the collector comprises a charging device having anelectrode, a high voltage power source coupled to the charging deviceand a spraying device having a spray nozzle. A tip of the electrodecreates an electric field defining a charging point that the air passesthrough between the aerosol entry port and the sample substrate. In thisregard, the sample substrate is held at an electric potential that isdifferent from the electric potential of the charging point duringparticulate collection. The spraying device sprays a fluid from thespray nozzle over the collection area of the sample substrate. Thesprayed fluid is specifically selected to prepare the collected samplefor subsequent evaluation.

In certain illustrative embodiments of the present invention, thecollector comprises a pump that pulls air into the collector housingthrough the aerosol entry port and through the passageway such thatparticulates within the air drawn through the passageway are collectedon a collection surface of a sample substrate, which is positionedwithin the sample substrate receiving area of the collector. The pumpfurther evacuates the air stripped of particulates from the collectorhousing.

According to still further aspects of the present invention, a tip ofthe electrode of the charging device is positioned within the passagewayso as to create an electric field defining a charging point that the airpasses through between the aerosol entry port and the sample substrate.Additionally, the substrate is held at a neutral or opposite chargerelative to the charge on the electrode. In this manner, particulatesare collected on a collection surface of the sample substrate by drawingthe particles to the substrate via the electric field when the aerosolis forced to flow near the substrate, e.g., via the pump. Moreover, thespray nozzle of the spraying device is positioned within the passagewaybetween the electrode tip and the sample receiving area. A high voltageis applied to the spraying device, e.g., at least during sprayingoperations where the spraying device sprays a fluid from the spraynozzle over the collection area of the sample substrate.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic illustration of a device that combineselectrostatic collection of aerosol particles and electrohydrodynamicspraying of fluid, according to various aspects of the presentinvention;

FIG. 2 is a view looking up from the bottom toward an exit end of aspray discharge nozzle of a spraying device according to various aspectsof the present invention;

FIG. 3 is a schematic illustration of a beveled needle spraying a samplesubstrate within a collector according to various aspects of the presentinvention;

FIG. 4 is a schematic of an illustrative holder for a vibrating motorassembly that vibrates a sample substrate for disaggregation accordingto various aspects of the present invention;

FIG. 5 is a schematic of another illustrative holder for a vibratingmotor assembly that vibrates a sample substrate for disaggregationaccording to various aspects of the present invention;

FIG. 6 is a schematic of still another illustrative holder for avibrating motor assembly that vibrates a sample substrate fordisaggregation according to various aspects of the present invention;

FIG. 7 is a schematic view of a vibrating motor that vibrates a samplesubstrate for disaggregation according to various aspects of the presentinvention; and

FIG. 8 is a schematic illustration of a motor positioned to vibrate asample substrate within a device that combines electrostatic collectionof aerosol particles and electrohydrodynamic spraying of fluid,according to various aspects of the present invention.

MODES FOR CARRYING OUT THE INVENTION

Many current technologies for the monitoring and analysis of impuritiesrequire that a sample is first collected and concentrated onto a samplesubstrate. In this regard, according to various aspects of the presentinvention, a small area electrostatic collector is provided, which canbe used to remove particulates including bioaerosol particles from theair and deposit them into a small area on a solid substrate. Particlesare charged prior to being deposited on the substrate usingelectrostatic forces caused by an electric field generated within thecollector. More particularly, electrostatic collection of aerosolparticles is implemented by utilizing a charge source of highelectrostatic potential (e.g., in the range of 8-12 kilovolts), such asa charged wire or charged needle, to charge aerosol particles that passthe charge source. The charged aerosol particles are then attracted to asubstrate collection surface that is held at an electric potentialdifferent from the electric potential of the charge source duringparticulate collection. For instance, in some embodiments, the substratecollection surface is electrically grounded.

According to further aspects of the present invention, in numerousembodiments, the collector further comprises an electrohydrodynamicspraying device. Electrohydrodynamic spraying places a highelectrostatic potential (e.g., measured in kilovolts) on conductivemicro-tubing. Fluid is injected through the conductive micro-tubing suchthat a charge is transferred from the micro-tubing to the fluid. Thetransfer of charge to the fluid leads to the dispersion of the fluid inair as sub-micron diameter aerosol droplets.

According to various aspects of the present invention, devices andcorresponding methods are provided for sample collection andpreparation. In this regard, the electrostatic collection of aerosolparticles and electrohydrodynamic (EHD) spraying of fluid are combinedin a single system so that a sample collected electrostatically can havefluid applied directly thereto. In exemplary implementations,electrostatic collection of biological aerosols is accompanied byperiodic or simultaneous injection of fluid, e.g., in order to prepare acollected sample for subsequent analysis. Accordingly, the collectorprovides integrated aerosol sampling and pretreatment of the collectedsample with appropriate fluids. In other embodiments, sample preparationis further carried out by using a mechanical aid to disaggregateclusters of collected biological material.

Referring now to the drawings and in particular to FIG. 1, a small areaelectrostatic aerosol collector 10 is illustrated according to variousaspects of the present invention. In general, the collector 10 includesa collector housing 12 that contains electrostatic collectioncomponents, electrohydrodynamic spraying components and samplecollection components as will be described in greater detail herein. Theillustrated housing 12 defines a collector head base, although thehousing 12 can alternatively take on other configurations. An aerosolentry port 14 serves as an inlet that provides an inlet for air to flowfrom outside of the collector housing 12 to the inside of the housing12. The aerosol may be any source of gas laden with particulates to beremoved from the aerosol. A typical application, however, comprisessampling ambient air.

Air to be sampled enters the aerosol entry port 14 and is moved througha passageway 16 within the housing 12. As illustrated, the passageway 16(hereinafter, “passageway” or “ductwork”) is implemented by ductworkthat includes a generally tube-shaped passageway between the aerosolentry port 14 and a sample substrate receiving area. However, in otherembodiments, the ductwork passageway 16 is implemented in alternateways. As the air passes through the ductwork 16 toward the samplesubstrate receiving area, particulates are separated from the air, andthe air (stripped of the collected particles) is exhausted from thehousing 12 through an exit port. For instance, in the illustrativeexample, ambient air is drawn into the collector 10 through the aerosolentry port 14. The air is further drawn through the ductwork 16 and isexhausted from the collector 10 via an exhaust port 18. In severalembodiments, the air is drawn through the collector 10 using a pump 19.In this regard, the exhaust port 18 should be suitably located dependingupon the manner in which the sample collection process is implemented,e.g., above the sample substrate receiving area or below the samplesubstrate receiving area.

As illustrated, the sample substrate receiving area is implemented by acollection station 20. In general, the sample collection station 20 isutilized to collect samples of particulates extracted from the airpassing through the ductwork 16 onto a collection surface 22A of asample substrate 22 positioned within a sample collection area 24 of thehousing 12.

The housing 12 is comprised of any suitable nonconductive material ormaterials, e.g., constructed of a polyacetal, such as Delrin® acetalresin by E. I. du Pont and Company of Wilmington, Del. Delrin is atrademark of E. I. du Pont de Nemours and Company. In many embodiments,the aerosol entry port 14 and the ductwork 16 also each comprise anonconductive material, such as a polyacetal.

In some embodiments, the sample substrate 22 comprises an aluminizedMylar tape. The tape is oriented such that the aluminum side of the tapedefines a collection surface 22A that faces the ductwork 16 so that theparticulates are collected onto the aluminum. In numerous embodiments,the aluminized Mylar tape is integrated into a cassette or other formatfor implementation as an automated sampling system, e.g., by using asuitable roller and tensioner for winding and unwinding the Mylar tape.In other embodiments the sample substrate 22 comprises a slide such asan aluminum coated glass slide. In several embodiments, the slide issecured within the sample collection area 24 of the housing 12 using anysuitable means, e.g., using a spring biased retainer that secures theslide under an air exit in the passageway of the ductwork 16 such thatthe slide can be easily replaced, changed, or both.

Electrostatic Collection

A charging device 30 is positioned so as to create an electric fielddefining a charging point that the air passes through between the inletof the aerosol entry port 14 and the sample substrate 22. In anillustrative implementation, the charging device 30 comprises at leastone electrode 32, such as a charging wire. In many embodiments, theelectrode 32 comprises a tungsten electrode or other suitable materialthat terminates in a point or generally pointed end. As such, theelectrode 32 may also be referred to herein as a charging needle tocharacterize the electrode as being generally “needle shaped” accordingto various aspects of the present invention. In general, a dull tip onthe electrode may result in less efficient operation, whereas arelatively sharper tip may be more efficient. However, the specificapplication will dictate the requirements of the electrode geometry.

In the illustrative implementation, the electrode 32 passes through theductwork 16 at an angle such that its tip extends generally in themiddle of the passageway defined by the ductwork 16. By way ofillustration, in some embodiments, the electrode 32 is positionedapproximately 12 millimeters (mm) above the sample substrate 22 within apassageway of the ductwork 16. In numerous embodiments, the diameter ofthe passageway has dimensions of approximately 6 mm.

Moreover, the electrode 32 is supported by a collection needle holder34. In the illustrative implementation, the collection needle holder 34extends outside of the housing 12. This approach facilitates assembly,replacement, or both of different types of electrodes 32. Moreover, thisapproach facilitates positioning of the electrode 32 for desiredoperation, e.g., using an appropriate adjustment mechanism 36. In thisregard, the adjustment mechanism 36 allows for user-adjustable control,e.g., of the angle of the electrode 32, the positioning of the electrode32 within the ductwork 16, etc. The electrode 32 is connected to a highvoltage power source 38, e.g., that generates approximately 8-12kilovolts of direct current (dc) power, as will be described in greaterdetail below. In an illustrative example, the high voltage source 38creates a high voltage signal that is connected to the collection needleholder 34 (e.g., a stainless steel housing) that couples the highvoltage to the electrode 32. However, other configurations mayalternatively be implemented.

According to various aspects of the present invention, the collectionsurface 22A of the sample substrate 22 is located in close proximity toan air exit end of the passageway 16, which is positioned opposite theaerosol entry port 14 in the illustrative example. Moreover, thecollection surface of the sample substrate 22 is held at an electricpotential different from the electric potential of the charge source,e.g., the electrode 32 during particulate collection. In an exemplaryimplementation, at least the collection surface 22A of the samplesubstrate 22 is held at a neutral (e.g., electrically grounded) oropposite charge relative to the electrode 32. For example, in someembodiments, a grounding ring 42, e.g., an electrically grounded copperring, is coupled to an aluminum collection surface of the exemplarysample substrate 22. In numerous embodiments, the grounding ring 42 isgrounded using a suitable ground connection and enables the samplereceiving surface of the sample substrate 22 to be grounded relative tothe electric field generated by the electrode 32. In this regard, inseveral embodiments, direct physical contact is provided between thegrounding ring 42 and the collection surface 22A of the sample substrate22 to facilitate desired grounding.

According to further aspects of the present invention, anelectrohydrodynamic sleeve 44, such as an electrically groundedstainless steel sleeve, is provided around yet spaced apart from the endsection of the ductwork 16, and a head seal 46, such as a rubber gasket,is positioned between the grounding ring 42 and the electrohydrodynamicsleeve 44. In an exemplary implementation, the head seal 46 comprises agasket that isolates the region of the sample substrate 22 oriented withrespect to the end of the ductwork 16 for receiving particulates so thatthe collection area is isolated during sample collection, e.g., so thatpreviously collected samples are not contaminated by particulatescollected during a current collection process. Thus, multiple collectionsites are possible on a single sample substrate.

In operation, the pump 19 pulls air into the collector housing 12through the aerosol entry port 14. The air is drawn by the pump 19 fromthe inlet of the aerosol entry port 14 through ductwork 16. A tip of theelectrode 32 associated with the charging device 30 is positioned withinductwork 16 so as to create an electric field defining a charging pointthat the air passes through between the aerosol entry port 14 and asample substrate 22. Further, the collection surface 22A of a samplesubstrate 22 positioned within the collector station 20 is held at anelectric potential that is different from, e.g., held at a neutral oropposite charge relative to, the electric potential of the chargingpoint defined by the charging device 30 during particulate collection.The charged particles are attracted to, and are thus likely to adhereto, the collection surface 22A, thus providing improved collectionefficiency. Particulates are thus collected by containing the aerosol ina small area within the ductwork 16 and by forcing the aerosol to flownear the sample substrate 22 such that the charged particulates areattracted to the collection surface 22A of the sample substrate 22.

In many embodiments, the pump 19 further evacuates the particulate-freeair through the exit port 18. The pump 19 evacuates the air out of thesample collection station 20 and, optionally, out of the housing 12 toatmosphere. In this regard, the sample substrate 22 is positioned inclose proximity to the exit end of the ductwork 16 and the main pressurechange occurs at the gap between the ductwork 16 and the samplesubstrate 22, which may be barely big enough for the air to passthrough. In an illustrative example, the pump pulls betweenapproximately 1-3 liters of air per minute.

Particulates in the air are charged when they pass the electrode 32 andare attracted to the oppositely charged (or grounded) collection surface22A of the sample substrate 22. The remaining air is evacuated, as notedin greater detail herein. In this regard, air is not required to flowunder/behind the sample substrate 22. Rather, air may flow under/behindthe sample substrate 22 for exhausting from the collector 10 housing 12.Alternatively, air may be directed from above the collection surface 22Aof the sample substrate 22, so as to be drawn through an air passageway,e.g., the passageway 18, to a location outside of the collector housing12. Evacuation of air from above the sample collection surface 22A maybe of interest, for example, where the sample substrate is implementedusing automated processes, such as collection tape based systems.

When high dc voltage, e.g., a dc voltage in the range of 1,600 volts toover 11,000 volts, is applied to the electrode 32, a corona dischargeextends from the point of the electrode 32 (point emission electrode) tothe substrate 22. The collection surface 22A of the sample substrate 22is grounded or held at a charge opposite of the electric field generatedwithin the ductwork 16. As such, the sample substrate 22 forms adischarge electrode. An electric field charges particulates suspendedwithin the air stream passing through the ductwork 16 towards the samplesubstrate 22. Moreover, precipitation takes place between the electrode32 and the sample substrate 22, and the particulates within the aerosolare collected onto the sample receiving surface of the sample substrate22.

According to various aspects of the present invention, no heat or otherfeature is required to prevent precipitation in the ductwork 16 itself.Moreover, the material of the ductwork 16, e.g., Delrin® acetal resin inthe above example, is useful in reducing, preventing or otherwiseinhibiting any potential precipitation/buildup in the passageway.Moreover, the collector 10, according to various aspects of the presentinvention, does not necessarily run in a continuous manner. Rather,there may be stops in the collection process, which allows time for theelectrode 32 to dissipate. Since the field generated by the electrode 32has time to dissipate, the potential for contamination build up withinthe collector is minimized.

Electrohydrodynamic Spraying

The collector 10 also includes an electrohydrodynamic spraying device50. The illustrated electrohydrodynamic spraying device 50 comprises anelectrohydrodynamic spray nozzle 52, e.g., a conductive micro tubing,for spraying fluid towards the sample area. For instance, asillustrated, the spray nozzle 52 extends into the passageway between thetip of the electrode 32 and the sample collection surface.

The spraying device 50 further comprises an electrohydrodynamic nozzleholder 54 that passes through the body of the housing 12. The nozzleholder 54 is charged to a high voltage in a manner analogous to thatdescribed in reference to the Electrostatic Collection above. In anexemplary implementation, an adjustment device 56 is provided to adjustthe position of the nozzle holder 54 and hence, the spray nozzle 52within the ductwork 16 to facilitate proper setup, also in a manneranalogous to that described in reference to the Electrostatic Collectionabove. In alternative implementations, the adjustment device 56 iseither optional or not implemented. For instance, depending upon theimplementation, the adjustment device 56 can be utilized for one or moreof the following: to adjust the angle of the spray nozzle 52 within theductwork 16, to adjust the amount of penetration of the nozzle into theductwork 16 or to facilitate user replacement of the spray nozzle 52.

A high voltage source 58 is provided to couple a high voltage to thespraying device 50 and corresponding spray nozzle 52. In an illustrativeexample, the first and second power supplies 38, 58 comprise differentpower supplies. For instance, two power supplies are be utilized intandem. Under this configuration, the first and second power suppliesgenerate voltages relative to a different reference potential.Alternatively, the first and second power supplies 38, 58 can eachgenerate a high voltage with respect to a common ground reference. Asyet another alternative example, the first and second power supplies 38,58 are implemented by a single power source that is optionally scaled toprovide the appropriate voltage to the electrode 32 and the spray nozzle52. Still further, as will be described in greater detail below, incertain illustrative embodiments, the voltage of each of the first andsecond power supplies 38, 58 is controllable, e.g., switchable betweentwo or more voltages. For instance, a controller may control eachvoltage source 38, 58 for operation between an off state, a high voltagestate and an operating state, where the output at the high voltage stateis a relatively high voltage that is different from (e.g., less than)the operational voltage setting.

A fluid tubing 60 feeds fluid from a suitable source 62 such as asyringe pump, into the spraying device 50, e.g., using a suitablefluidics fitting 64. The end of the spraying device 50 proximate to thefluidics fitting 64 thus defines a fluid inlet to the spraying device50. The fluid is injected from the fluidics fitting 64 through aspray-fluid passageway 66 in the nozzle holder 54, e.g., a conductivemicro-tubing such as stainless steel. Electrohydrodynamic sprayingplaces a high electrostatic potential (e.g., measured in kilovolts) onthe spray-fluid passageway 66. In response thereto, a charge istransferred from the spray-fluid passageway 66 to the fluid. The spraynozzle 52 sprays the charged fluid towards the sample collection area24. The charge in the fluid disperses the fluid in air as aerosoldroplets with sub-micron diameters.

According to various aspects of the present invention, particulates arecollected on a collection surface 22A of the sample substrate 22 bycontaining the aerosol in a small area within the ductwork 16 and byforcing the aerosol to flow near the substrate via the pump 19.Additionally, the spraying device 50 sprays a fluid over the collectionarea 22A of the sample substrate 22, where the fluid is specificallyselected to prepare the collected sample for subsequent spectroscopicevaluation.

There are several benefits to combining electrostatic collection andelectrohydrodynamic spraying into a single collection system. Forinstance, the collected sample does not have to be moved to a samplepreparation station in order to suitably prepare a sample of analysis.Such an arrangement saves not only time, but also the space within asystem that would otherwise be required for separate sample collectionand preparation stations.

According to still further aspects of the present invention, thecollector 10 includes a controller 70, which is coupled to the chargingdevice 30, the spraying device 50, or both. The controller 70 can thuscontrol the charge device 30 and the spraying device 50 in any number ofsuitable manners. In certain embodiments, the controller 70 alsocontrols aspects of sample substrate preparation, e.g., by advancing orotherwise controlling a mechanism to wind a sample collection tape intosuitable position for sample collection. By way of a first illustration,the controller 70 controls the collector 10 such that collection andspraying takes place in an alternating fashion, i.e., collect for aperiod, spray for a period, collect again, spray again, etc. As yetanother alternative example, the controller 70 controls the collector 10such that sample collection and spraying occurs effectively orsubstantially simultaneously, e.g., wherein particles may interminglewith the fluid droplets in the air before accumulation on the collectionsurface 22A of the sample substrate 22.

In practice, specific geometric configurations and operating conditionsmay provide more optimal response characteristics, e.g., to allow forelectrostatic collection and electrohydrodynamic spraying to be used inthe same nozzle. For instance, as illustrated, the fluid injectionnozzle 52, e.g., a metal micro-tubing, e.g., having an outside diameterof approximately 500 microns, is placed below the electrostatic chargingelectrode 32. More particularly, the exit end of the spray nozzle 52 iscloser to the collection area 22A of the sample substrate 22 than thetip of the electrode 32. In a further illustrative exemplaryimplementation, the electrode 32 and the exit end of the spray nozzle 52is spaced apart by a predetermined distance to prevent conduction therebetween. In an illustrative example, a separation of at least 6millimeters may be sufficient to avoid conduction between the two. Oneexemplary approach to conserve space is to place a bend in the spraynozzle 52 such that the exit end of the spray nozzle 52 is sufficientlyseparated from the electrode 32.

For example, as illustrated, the spray nozzle 52 of the spraying device50 includes a bend along its length positioned within the ductwork 16such that the spray nozzle 52 enters the ductwork 16 at an angle, e.g.,non-perpendicular to the wall of the ductwork 16, and an exit of thespray nozzle 52 points substantially down towards the collection area ofthe sample substrate 22. In an illustrative example, the spray nozzle 52contains a bend of an obtuse angle, e.g., a bend at an obtuse angle in ametal micro-tubing for dispensing a fluid towards the sample area. Inthis regard, the spray nozzle 52 comprises an end portion 52C forinjecting fluid that points towards the grounded collection surface 22Aof the sample substrate 22. In the illustrative example, the end portion52C is arranged substantially parallel to the walls of the ductwork 16proximate to the sample substrate 22. Moreover, in certain illustrativeembodiments, the end portion 52C extends a distance, e.g., approximately1 millimeter, and can optionally include a bend so that the opening ofthe spray nozzle 52 points towards the deposition surface of the samplesubstrate 22.

In yet another illustrative example, electrostatic collection occurswhen the tip of the electrode 32 is approximately 12 mm above thecollection area 22A of the sample substrate 22. There may be at least 6mm separation between the tip of the electrode 32 and the exit 52C ofthe spray nozzle 52. Thus, the exit 52C of the spray nozzle 52 ispositioned within 6 mm of the collection surface 22A of the samplesubstrate 22.

As yet a further illustrative example, the electrode 32 and the spraynozzle 52 enter the ductwork 16 from different, e.g., substantiallyopposite sides of the ductwork 16, such that only the tip of theelectrode 32 and the exit end of the spray nozzle 52 extend at leastsubstantially to a position above the center of the collection area ofthe sample substrate 22. For instance, the electrode 32, e.g., acharging needle, and the spray nozzle 52, enter the ductwork 16 fromopposite sides such that only the tip of the charging electrode 32 andthe exit end of the spray nozzle 52 overlap in the ductwork 16 above thecenter of a collection region associated with the collection surface 22Aof a sample substrate 22 loaded into the collection station 20.

For both electrostatic collection and electrohydrodynamic spraying, thehighest charge density is centered above the target zone defined by thecollection surface 22A. This presents the problem of charge transferbetween the charged elements, i.e., the electrode 32 and the spraynozzle 52. However, placing the fluid injection nozzle below theelectrostatic charge needle, maintaining suitable separation between thecharged elements to prevent conduction there between, suitably reducingthe potential difference between the charged elements, or combinationsthereof, suitably addresses these charge transfer problems.

As noted in greater detail herein, separation of the conductive elementscan optionally be achieved by placing a bend in the fluid injectionnozzle such that the tip of the fluid injection nozzle is sufficientlyseparated from the tip of the charging needle. Additionally, byinserting the charging needle and the fluid injection nozzle fromopposite sides, only the tips of the charging needle and fluid injectionnozzle overlap, e.g., in the center of the collection region. Moreover,according to certain embodiments of the present invention, thecontroller 70 holds the charge device 30 at a high voltage when thespraying device 50 is being operated and the controller 70 holds thespraying device 50 at a high voltage when the charge device 30 is beingoperated where the voltages are selected to avoid conduction between thecharge device 30 and the spraying device 50. Thus, even when only one ofthe two elements, e.g., the charge device 30 and spraying device 50, isoperating, the other element may still be held at a high electrostaticpotential (although not necessarily at its operating potential) in orderto prevent conduction between the two.

Spray Nozzle

For electrohydrodynamic spraying, fluid is pumped through the spraynozzle 52. Voltage, e.g., from the voltage source 58, is applied to thespray nozzle 52, e.g., a metal micro-tube, which causes fluid that hasentered the spraying device 50 via the fluid tubing 60 to form a Taylorcone as it emerges and disperse as aerosol droplets.

In conventional electrohydrodynamic spraying applications, consistentelectrohydrodynamic spraying can be achieved, e.g., in a “free space”configuration, e.g., with no surfaces within several centimeters of thecharged tubing of the spray nozzle 52 or the dispersed aerosol. However,the space within the collector 10 about the spray nozzle 52 is a “closedspace.” As such, conventional electrohydrodynamic spray techniques mayresult in the injected fluid flowing as a stream towards this surfaceinstead of forming the Taylor cone and dispersing.

According to various aspects of the present invention, the spray nozzle52 is utilized for electrohydrodynamic spraying of a fluid inside anenclosed area of the ductwork 16. In this regard, in an illustrativeexample, the diameter of the ductwork is on the order of 6 mm, howeverother dimensions may alternatively be implemented.

However, according to various aspects of the present invention,consistent electrohydrodynamic spraying is achieved despite beingpositioned inside an enclosed cylinder that has an inner diameter ofonly several millimeters. To achieve consistent electrohydrodynamicspraying, as noted above, the spray nozzle 52 is implemented in someembodiments using metal micro-tubing. Moreover, the exit 52C of thespray nozzle 52 is bent so as to point towards the grounded depositionsurface, i.e., the exit 52C of the spray nozzle 52 is parallel to thewalls of the cylinder shaped ductwork 16 and is perpendicular to thesample substrate 22. As also noted in greater detail herein, inillustrative embodiments, the spray nozzle 52 enters the cylinderthrough a side wall; however, the tip (e.g., approximately 1 mm from theexit end) is bent so that it points towards the deposition surface forflowing the liquid.

Referring to FIG. 2, a view is presented looking up from the bottom ofthe collector 10, according to further aspects of the present invention.As schematically represented, in this illustrative but non-limitingimplementation, the spray nozzle 52 is positioned inside two cylinders,which are concentric. More specifically, the spray nozzle 52 ispositioned within an outer cylinder 72 and inner cylinder 74. The innerconcentric cylinder 74 is closest to the charged injection tubing, isgenerally cylindrical in shape and is constructed so as to be anon-conductive cylinder, e.g., a Delrin or similar material. In thisregard, the inner concentric cylinder (Delrin collector head) comprisesthe ductwork 16 and may thus have a diameter in an exemplaryimplementation, on the order of approximately 6 mm. The nonconductivecylinder 74, which is closest to the charged injection fluid tubing 60and corresponding spray nozzle 52, defines a collector head and isnon-conductive in order to insulate the charged fluid tubing 60 andspray nozzle 52.

The outer cylinder 72 comprises an external conductive cylinder. Forinstance, referring back to FIG. 1, the outer cylinder 72 may beimplemented as the electrohydrodynamic sleeve 44, which is spaced fromand optionally concentric with the ductwork 16 proximate to the samplecollection area. In the illustrative example, the electrohydrodynamicsleeve 44 is electrically grounded and extends sufficiently within thehousing 12 to surround the exit end of the spray nozzle 52. Under thisillustrative configuration, the spraying device 50 produces a consistentaerosol dispersion and electrohydrodynamic spraying produces adispersion of sub-micron diameter aerosol droplets, even at low fluidflow rates, e.g., on the order of micro liters per minute.

As described more fully herein, the use of a bent metal micro-tubing forflowing the liquid sample, the use of two concentric cylinders, aninternal non-conductive cylinder and an external conductive cylinder,and combinations thereof, provide the device with the ability to achieveconsistent aerosol spraying, as described more fully herein.

Sample Preparation

According to various aspects of the present invention,electrohydrodynamic spraying of fluids may be applied to the preparationof dry, collected biological aerosol samples. In this regard, thespraying of fluids can disaggregate clusters of the collected biologicalmaterial and/or desalinization of the collected biological materials.

Biological aerosols collected from the atmosphere have at least twocharacteristics that make them difficult to analyze using spectroscopictechniques such as Raman spectroscopy. The aerosol particles are oftenagglomerations of biological materials, e.g., several bacterial cellsagglomerated into a cluster. In Raman analysis, it is beneficial toprobe individual cells or, at least, small clusters (0.5-1.5 micrometerdiameters). Moreover, the biological aerosol particles also often haveinorganic salts intermingled with the biological material of interest.Crystallized, polyatomic salts often have strong Raman responses thatmake the Raman spectrum of the biological material more difficult toanalyze. Therefore, it is beneficial to either separate the salts fromthe biological material or dissolve the salts prior to Raman analysissince the dissolved salts do not have a strong Raman response.

However, according to various aspects of the present invention,electrohydrodynamic spraying is utilized in the electrostatic aerosolcollector 12 as an effective means of accomplishing disaggregation ofclusters of the collected biological material, desalinization of thecollected biological materials, or both. Thus, electrohydrodynamicspraying according to various aspects of the present invention, providesa means of generating a dispersion of sub-micron diameter aerosoldroplets at low fluid flow rates, e.g., on the order of microliters perminute. This mist is generated by injecting the fluid across a largeelectrostatic potential (measured in kilovolts), with the injectionmicro-tubing at a raised potential and the target surface at electricalground. The generated dispersion spreads out over a sufficiently largearea that all of the collected aerosol particles can be covered withfluid in a single spray.

In an illustrative example, the fluid comprises a mixture of water withethanol, such as a mixture comprising water with 20-35% ethanol.However, other fluid mixtures may also be applicable.Electrohydrodynamic spraying could inject other fluids so long as enoughwater is available that the salts will dissolve in the fluid but also asufficient percentage of organic solvent is available in order toprevent the water soluble biological material from dissolving as well.

Electrohydrodynamic spraying onto biological clusters encourages theseclusters to separate, leading to significant separation of agglomeratedparticles, even within tens of seconds to minutes of spraying. Thedeposited fluid is also able to evaporate quickly, without pooling intolarge droplets that might lead to significant movement of the biologicalmaterial on the substrate.

Applications of various aspects of the present invention find use forexample, in the treatment of collected biological aerosol samples inpreparation for spectroscopic analysis, e.g., Raman analysis. Otheranalysis techniques that benefit from analyzing separated biologicalparticles and/or biological particles free of salt would also benefitfrom applying various aspects of the invention as set out in greaterdetail herein.

ILLUSTRATIVE EXAMPLES

As an illustrative example, a 1 milliliter (ml) plastic syringe, e.g.,by Becton, Dickinson and Company of Franklin Lakes, N.J. was tested withan 18-gauge flat tip needle utilized to implement the spray nozzle 52,e.g., by Engineered Fluid Dispensing (a Nordson Corporation of Westlake,Ohio) at a vertical distance of approximately 1 inch (2.54 centimeters)from the sample substrate 22. A solution of 50% EtOH, e.g., 20 mlethanol and 20 ml H₂O, was sprayed at an infuse rate at 0.5 microlitersper second (μl/sec) (30 μl/min). In this illustrative implementation, aTaylor cone and fine mist spraying was achieved at 5-6 kilovolts (kV).If the voltage is too low or too excessive, the spray pattern qualitycan deteriorate, e.g., into a spitty spray, split into a multi sectionbeam, etc. Lowering the infusion rate, e.g., to 0.25 μl/sec (15 μl/min)at 5-6 kV resulted in even a finer spray. Under this configuration, theoutside diameter of the spray was about 15 mm.

Reducing the distance of the needle spray nozzle 52, e.g., down toapproximately half an inch (12.7 mm) above the sample substrate 22resulted in a well-sprayed pattern at 4-5 kV. Moreover, spraying wassuccessful at both 0.25 μl/sec and 0.5 μl/sec. In another illustrativeexample, a 5.0 μl dose appeared to wet the sample area well, e.g.,enclosed in a 6 mm diameter.

A small, e.g., about 5 mm, length of flexible tubing or other suitablematerial is optionally placed over the flat tip of the needle. Moreover,the needle is optionally turned horizontally, e.g., using an appropriateadjustment mechanism 56. However, when using the needle turnedhorizontally, a bend about its tip (e.g., 52C of the spray nozzle 52) ofsubstantially 90 degrees is preferable. However, the bent tip may skewthe spray pattern away from the high voltage field, even at lowervoltages.

In general, spray divergence may be dependent upon a number of factors,including for example, the needle diameter. Moreover, the flow rate willdetermine wetting. For instance, a flow rate of 1 μl/min may spray finebut result in a wetting that is barely visible, e.g., compared to a flowrate of approximately 5 μl/minute, which may result in a wetting that isvisible on the surface of the sample substrate. Moreover, the flow ratemay affect that shape of the spray pattern. For instance, relatively lowflow rates may result in a wetting that is more elliptical in shape,whereas increasing the flow rate may eventually restore the shape of thesprayed area to a substantially circular pattern.

Still further, in certain embodiments, the needle sprays in air.However, a collar is optionally utilized, e.g., an insulation materialcan be placed over the sample substrate, such as to define a boundaryfor the spray pattern. In some embodiments, the ductwork 16 serves afurther purpose of defining a boundary for the spray pattern. In otherembodiments, a tube of conductive material forms a spray boundary and agrounding feature 44, which does not necessarily touch the samplesubstrate 22 and is described in greater detail herein.

Still further, by angling the needle implementing the spray nozzle 52into the ductwork 16, the pattern of spray on the sample substrate maybe made oblong, elliptical, etc. Still further, the needle end mayaffect spraying. For example, a hypodermic needle with a beveled exitaperture may affect the spray pattern. As such, the spray pattern of thespraying device may be controlled by at least one of the flow rate ofthe corresponding fluid, the angle of the needle implementing the spraynozzle 52 and the geometry of the spray nozzle end.

Referring to FIG. 3, when using a hypodermic needle as the spray nozzle52, the needle has a beveled needle exit at a first angle ANGLE 1 thatshould be accounted for when adjusting the needle to a correspondinginstallation angle ANGLE 2. For instance, a beveled needle achieves anoblong spray pattern having a long axis perpendicular to the needleaxis.

In an illustrative implementation, using a 20 mil (500 μm) outsidediameter spray nozzle 52 at an air flow rate of 3.0 l/min and a 25% EtOHfluid flow rate of 5.0 μl/min., a steady spray may be achieved from4.0-6.0 kV, with a largest spot of less than 5 mm at 4.5-5.0 kV. Underthis approach, a 5 mm spot may take less than 1 minute to dry. Adjustingthe spray nozzle 52 to about 1.5 mm from the edge, a nice spray may beachieved from 5.0-5.5 kV, almost covering the whole 6 mm spot.

Mechanical Aid to Disaggregate Clusters of Collected Biological Material

For the analysis of biological materials it is sometimes necessary tobreak up clusters of aggregated cells, or other biological material,into individual cells. According to various aspects of the presentinvention, such can be accomplished using electrohydrodynamic spraying(as described above), mechanical means, or both. As an illustrativeexample, a motor can be used to shake and separate such clusters byshaking the substrate they are collected on.

Biological material, such as bacterial cells, often aggregate intoclusters when it is dried. For some types of analyses, such as countingthe number of cells or microscopic analysis of individual cells, it isvaluable for such clusters to be broken up and for individual cells tobe separated. This can be done by shaking the substrate that containsthe clusters, which transfers the kinetic energy into the clusters. Thevibrations resulting from the kinetic energy separate the aggregatedcells from one another.

According to various aspects of the present invention, systems andmethods are provided for shaking the sample substrate and the clustersusing a motor, such as a cell phone vibration motor, as a compact andrelatively low power driver. Exemplary motors comprise, for example,Precision Microdrives #310-101 (a 10 mm diameter button-type at 12 kHz)and #304-002 (a 4 mm×8 mm off-center shift weight design).

In this regard, such a feature allows the cluster separation to beintegrated efficiently into an instrument, thus saving the time requiredto later perform the disaggregation process and also to save the spacetypically required to perform such a step at a separate station.

Referring to FIG. 4, a disaggregation holder assembly 80 is illustratedaccording to various aspects of the present invention. The assembly 80includes a top plate 82 that secures to a bottom plate 84, e.g., usingfasteners 86. In the exemplary illustrated implementation, the bottomplate 84 includes a channel 88 for receiving a motor, e.g., an eccentricmass vibrator motor 90 and a corresponding vibrator cap 92. The massvibrator motor 90 and a corresponding vibrator cap 92 are positioned inthe channel 88 and the top and bottom plates 82, 84 are joined andsecured together, e.g., using the fasteners 86. In an illustrativeimplementation, a spring plunger 94 feeds through the bottom plate 84into the motor. The spring plunger 94 retains the motor and allows forvariable vibration and amplitude control of the motor. Other holderassemblies may alternatively be implemented. The disaggregation holderassembly 80 is positioned so as to be able to transfer vibrationalenergy to the sample substrate, e.g., at least in the area of samplecollection. For instance, the disaggregation holder assembly 80 may bepositioned underneath the sample substrate 22 as shown below in FIG. 8.

Referring to FIG. 5, a simplified holder 100 is illustrated according tofurther aspects of the present invention. The illustrated holder 100comprises a mounting block 102 that holds a vibrator motor 104illustrated as a button vibrator motor. The mounting block 102 furtherpositions a vibrator cap 106 above the motor 104. Again, the holder 100is positioned so as to be able to transfer vibrational energy to thesample substrate, e.g., at least in the area of sample collection. Forinstance, the holder 100 may be positioned underneath the samplesubstrate 22 as shown below in FIG. 8.

Referring to FIG. 6, the vibrator motor 104 and vibrator cap of FIG. 5is illustrated according to further aspects of the present invention.The vibrator cap 106 comprises an extrusion 116 that localizesvibrations to the collection area of the sample substrate and furtherminimizes vibration induced into other components of the collector 10.The illustrated vibrator cap 106 further comprises a machined edge 118that sits in a slot in the holder 100 (FIG. 5) to prevent the vibratormotor 104 from walking around a slot in the holder 100. Similarly, thevibrator cap 106 includes an upper edge 120 that retains the motor 104in the holder 100. Analogously, the holder 100 is positioned so as to beable to transfer vibrational energy to the sample substrate, e.g., atleast in the area of sample collection. For instance, the holder 100 maybe positioned underneath the sample substrate 22 as shown below in FIG.8.

Referring to FIG. 7, an assembly 122 for the vibrator motor 104 andholder 100 for use with a sampling stage of the collector (10, FIG. 1)is illustrated according to further aspects of the invention. Theillustrated assembly 122 comprises the mounting block 102 that holds thevibrator motor 104. The mounting block 102 comprises substrate mountingsurface 126 that couples to the sample substrate 22. The mounting block102 also supports the vibrator cap 106 that retains vibrations of themotor and localizes vibrations as described more fully herein. Themounting block 102 also supports a vacuum chuck groove 130 and a springplunger 132 that retains the motor 104 and allows for variable vibrationand amplitude control of the motor 104. Still analogously, the holder100 is positioned so as to be able to transfer vibrational energy to thesample substrate, e.g., at least in the area of sample collection. Forinstance, the holder 100 may be positioned underneath the samplesubstrate 22 as shown below in FIG. 8.

Referring to FIG. 8, a collector system (10, FIG. 1) is illustratedaccording to various aspects of the present invention. The system isidentical to that described with reference to FIG. 1 with the additionof a motor and corresponding holder 80, 100 positioned under the samplesubstrate 22. As illustrated, the motor holder enables vibration of thesample substrate 22.

The description of the present invention has been presented for purposesof illustration and description, but is not intended to be exhaustive orlimited to the invention in the form disclosed. Many modifications andvariations will be apparent to those of ordinary skill in the artwithout departing from the scope and spirit of the invention. Elementsof the embodiments may be combined with elements of other embodiments tocreate further embodiments.

The terminology used herein is for the purpose of describing particularembodiments only and is not intended to be limiting of the invention. Asused herein, the singular forms “a”, “an” and “the” are intended toinclude the plural forms as well, unless the context clearly indicatesotherwise. It will be further understood that the terms “comprises”and/or “comprising,” when used in this specification, specify thepresence of stated features, integers, steps, operations, elements,and/or components, but do not preclude the presence or addition of oneor more other features, integers, steps, operations, elements,components, and/or groups thereof.

Having thus described the invention of the present application in detailand by reference to embodiments thereof, it will be apparent thatmodifications and variations are possible without departing from thescope of the invention defined in the appended claims.

1. An electrostatic aerosol collector (10) comprising: a collectorhousing (12); an aerosol entry port (14) that provides an inlet for airto flow from outside of the collector housing (12) to the inside of thehousing (12); a sample substrate receiving area (24) within thecollector housing (12) for receiving a sample substrate (22) including acollection area upon which particulates are collected; a passageway (16)between the aerosol entry port (14) and the sample substrate receivingarea (24); a charging device (30) having an electrode (32); a highvoltage power source (38) coupled to the charging device (30); and aspraying device (50) having a spray nozzle (52); wherein: a tip of theelectrode (32) creates an electric field defining a charging point inthe passageway (16) through which the air passes; the sample substrate(22) is held at an electric potential that is different from theelectric potential of the charging point during particulate collection;the spraying device (50) sprays a fluid from the spray nozzle (52) overthe collection area of the sample substrate (22), where the fluid isspecifically selected to prepare the collected sample for subsequentevaluation.
 2. The electrostatic aerosol collector according to claim 1,further comprising: a controller (70) for controlling the chargingdevice and the spraying device such that the charging device andspraying device operate in alternating fashion.
 3. The electrostaticaerosol collector according to claim 2, wherein: the controller holdsthe charging device at a high voltage when the spraying device is beingoperated at an operating potential of the spraying device, and thecontroller holds the spraying device at a high voltage when the chargingdevice is being operated at an operating potential of the chargingdevice, wherein: the high voltage of the spraying device is selected toavoid conduction between the charging device and the spraying device,and the high voltage of the charging device is selected to avoidconduction between the charging device and the spraying device.
 4. Theelectrostatic aerosol collector according to claim 3, wherein: the highvoltage set by the controller to hold the charging device is less thanthe operating potential of the charging device; and the high voltage setby the controller to hold the spraying device is less than the operatingpotential of the spraying device.
 5. The electrostatic aerosol collectoraccording to claim 1, further comprising: a controller (70) forcontrolling the charging device and the spraying device such that thecharging device and spraying device operate substantiallysimultaneously.
 6. The electrostatic aerosol collector according toclaim 1, wherein: a high voltage source (58) is coupled to the sprayingdevice; and at least 6 millimeters separates the spray nozzle from theelectrode.
 7. The electrostatic aerosol collector according to claim 7,wherein: the spray nozzle of the spraying device includes a bendtherein; the bend of the spray nozzle is along the length of the spraynozzle, the spray nozzle is positioned within the passageway such thatthe spray nozzle enters the passageway at an angle, and an exit (52C) ofthe spray nozzle points substantially down towards the collection areaof the sample substrate.
 8. The electrostatic aerosol collectoraccording to claim 1, wherein: an exit (52C) of the spray nozzle iscloser to the collection area of the sample substrate than a tip of theelectrode.
 9. The electrostatic aerosol collector according to claim 1,wherein: the electrode and the spray nozzle enter the passageway fromsubstantially opposite sides of the passageway such that only a tip ofthe electrode and an exit (52C) of the spray nozzle extend at leastsubstantially to the center of the passageway, above of the samplecollection area.
 10. The electrostatic aerosol collector according toclaim 1, wherein: the spray nozzle is enclosed in close proximity to anonconductive cylinder (74); and the nonconductive cylinder ispositioned within a conductive cylinder (76).
 11. The electrostaticaerosol collector according to claim 1, wherein: the spray nozzle is ina closed space, positioned within at least two concentric cylinders,including an inner concentric cylinder that is a non-conductive cylinder(74) arranged to insulate the charged spray nozzle and the outerconcentric cylinder comprises a conductive cylinder (76).
 12. Theelectrostatic aerosol collector according to claim 11, wherein the outerconcentric cylinder defines a grounded sleeve that is spaced from theinner cylinder and surrounds an exit (52C) of the spray nozzle.
 13. Theelectrostatic aerosol collector according to claim 1, wherein: the fluidsprayed by the spraying device at least one of: disaggregates clustersof the collected biological material and desalinizes the collectedbiological materials collected within the collection area of the samplesubstrate.
 14. The small area electrostatic aerosol collector accordingto claim 1, wherein: the fluid injected by the spraying device comprisesat least water and ethanol.
 15. The electrostatic aerosol collectoraccording to claim 1, wherein a spray pattern of the spraying device iscontrolled by at least one of: the flow rate of the corresponding fluid;the angle of the needle implementing the spray nozzle; and the geometryof the exit (52C) of the spray nozzle.
 16. The electrostatic aerosolcollector according to claim 1, further comprising: a motor positionedunder the sample substrate that is operable to vibrate so as to causedisaggregation of clusters of the collected biological materialcollected within the collection area of the sample substrate.
 17. Theelectrostatic aerosol collector according to claim 1, furthercomprising: a disaggregation holder assembly (80) positioned so as to beable to transfer vibrational energy to the sample substrate, thedisaggregation holder assembly comprising: a top plate (82) that securesto a bottom plate (84) such that a channel (88) is positioned betweenthe top plate and the bottom plate; an eccentric mass vibrator motor(90) received in the channel between the top plate and the bottom plate;and a spring plunger (92) fed through the bottom plate so as to allowfor variable vibration and amplitude control of the eccentric massvibrator motor.
 18. The small area electrostatic aerosol collectoraccording to claim 1, further comprising: a holder (100) positioned soas to be able to transfer vibrational energy to the sample substrate,the holder comprising: a mounting block (102) that holds a vibratormotor (104); and a vibrator cap (106) supported by the mounting blockover the motor.
 19. The small area electrostatic aerosol collectoraccording to claim 18, wherein: the vibrator cap further comprises anextrusion (116) that localizes vibrations to the collection area of thesample substrate and further minimizes vibration induced into thecollector.
 20. The small area electrostatic aerosol collector accordingto claim 18, wherein the vibrator cap further comprises: an edge (118)that sits the housing to prevent vibrations from walking around theholder; and an upper edge (120) that retains the motor in the holder.21. The small area electrostatic aerosol collector according to claim 1,further comprising: an assembly (122) positioned so as to be able totransfer vibrational energy to the sample substrate, the assemblycomprising: a mounting block (102) having a substrate mounting surface(126) that couples to the sample substrate and a vacuum chuck groove(130); a vibrator motor (104) held by the mounting block; a vibrator cap(106) supported by the mounting block that retains vibrations of thevibrator motor (104) and localizes vibrations to the area of the samplesubstrate; and a spring plunger (132) that retains the vibrator motorwith respect to the mounting block and allows for variable vibration andamplitude control of the vibrator motor.